Multi-walled carbon nanotubes (MWNTs) possess weak antimicrobial property. In this report, we demonstrate that the covalent immobilization of the antibiotic cefalexin via poly(ethylene glycol) as a linking agent improves the antimicrobial and anti-adhesive properties of MWNTs against both Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis). In particular, the MWNT-cefalexin composite showed 2-fold higher antimicrobial property than pristine MWNTs against S. aureus and B. subtilis. Moreover, the MWNT-cefalexin deposited film effectively inhibited cell adhesion. Given the simple, inexpensive procedures of our synthesis method, the MWNT-cefalexin composite has the potential to be used as an effective and economical antibacterial and anti-adhesion material for environmental and biomedical applications.